Botulinum neurotoxins (BoNTs) are classified by the Centers for Disease Control as one of the 6 highest-risk threat agents for bioterrorism (the Category A agents), due to their extreme potency and lethality, ease of production and transport, and need for prolonged intensive care. BoNTs have been produced and weaponized by rogue nations and deployed by terrorist groups. As a result of these threats, specific pharmaceutical agents are needed for prevention and treatment of intoxication. The only near term product for treatment of botulism that has been validated in animals and humans is antitoxin. Under previous NIAID funding, we have generated a potent human compatible recombinant monoclonal antibody based antitoxin for BoNT serotypes A, B, and E. The BoNT/A recombinant antitoxin is currently being developed under separate NIAID funding for human clinical trials. The overall goal of this proposal is to generate novel human compatible monoclonal antibodies (mAbs) that can be used to prevent and treat botulism caused by BoNT serotypes C, D, F, and G. Achievement of this goal requires three components: 1) determination of the extent of BoNT gene diversity of these 4 toxin serotypes (C, D, F, and G); 2) generation of panels of broadly neutralizing human compatible mAbs to the four BoNT serotypes; and 3) in vitro and in vivo characterization of mAbs with respect to serotype cross reactivity and toxin neutralization. These goals will be achieved by an inter-institutional team of botulism experts who have worked in this field for more than 13 years: James D. Marks, antibody engineering and Leonard Smith, BoNT vaccine development, toxin and toxin fragment generation and animal models of toxin neutralization. They will be assisted by an expert in microbial genetic characterization, Karen Hill, at Los Alamos National Laboratory, who will define the extent of toxin diversity to ensure that antibodies neutralize all possible toxin subtypes. At the end of the funding period we anticipate having generated a recombinant antitoxin for BoNT serotypes C, D, F, and G that can be transferred into the manufacturing and late stage development pathway. Combined with previous results, this will make available a safe, efficacious human compatible antitoxin for all seven BoNT serotypes.